This paper focuses on a functionalist analysis of the patterns followed when translating specific texts from English into Spanish. The original texts are written in English and, afterwards, translated to other languages. In this process, lexical variation may appear. The main objectives of this study are to determine whether English noun phrases have different lexical equivalents when translated into Spanish and whether this depends on the position of the head in the complex noun phrase. Other objectives of this paper are, on the one hand, to detect the role of the head and modifiers in English complex noun phrases when translated into the target language, and, on the other hand, to determine whether the specificity of nouns could be the cause of variation. The answer to these research questions will be useful for translators, communication specialists and scientists who use English and Spanish to communicate.